The present invention relates to a lighting apparatus for guiding light onto a light polymerizable piece to effect the hardening thereof.
Light devices have been deployed for, among other applications, dental applications in which a light polymerizable plastic is hardened by irradiation with light. In order to achieve a high light density, energy rich light sources are typically deployed such as halogen glow lamps, xenon photoflash, or even high-tension discharge lamps. The high-tension discharge lamps have, in fact, an especially high light intensity and, thereby, a correspondingly high light density. However, the operational tension reaches at least 3.5 kV and a corresponding activation device is required so that such lamps are not suitable for deployment in the dental practice, at least insofar as hand operable devices are concerned.
Numerous attempts have been undertaken to improve the light density of the known light apparatus in order to achieve a complete hardening of the deeper lying layers in a rapid manner. A long-time known, conventional lighting apparatus with a light intensity of, for example, 50 mW/cm2 produces, in fact, by a correspondingly longer light irradiation, a good surface hardening of the plastic or artificial piece which is to be polymerized. However, deeper lying layers are not at all hardened or, at most, only incompletely hardened. There arises a hardness gradient which leads to the result that the deeper lying, middle regions remain somewhat soft or that these regions are hardened completely at a time later than the complete hardening of the surface areas.
The known lighting apparatus lead to restoration results that are compromised by, or suffer from, in part, edge spalling problems. The known light hardenable plastics shrink slightly during the hardening process. With the known lighting apparatus, a complete hardening initially occurs first in the over/outer regions of the restoration piece. The thereafter following complete hardening of the deeper lying, central regions leads to contractions and, thus, to edge spalling formation.